Radar aiming angle analyzer



July 5, 1960 R. E. RAWLlNS 2,944,256

RADAR AIMING ANGLE ANALYZER Filed Aug. 11, 1955 3 Sheets-Sheet 1 INVENTOR. ROBERT E. RAwuNs E mi Q 7 m 2.86 322. 52 53 528% 5558: m A Q 292 58: m N Q N n fi y 1950 R. E. RAWLINS 2,944,256 RADAR AIMING ANGLE ANALYZER Filed Aug. 11, 1955 3 Sheets-Sheet 2 INVENTOR. ROBERT ERAWLINS mm m u%% V mmPJE m m mm 5 mm mm W in 56x6 5.5.. S23 mwmwasz 525mm 558mm. @N 292 582 w 5 mm flu E on July 5, 1960 R. E. RAWLINS RADAR AIMING ANGLE ANALYZER 3 Sheets-Sheet 3 522m 2. 52m .3 ma:

Filed Aug. 11, Q1955 m u mw A MR mi T R E B O R Agent n t d some ,R a 1) sin c ANALYZER lR rSbeit E aWlins'; "North Hollywood, Calift, assignor to Lockheed Aircraft 'Gorp'oration; Burbank, Calif.

riled Aug. 11, no, so. Na. szfifiozi 9 claims. (o1. 343* 113.)

,Th'is invefitio' relates", generally, to radar apparatus and trainee tater employs a directional energy beam to dea "'0 tion' information of a remote target and,

a bunny, to an analyzer for detecting the presor 'the energ beainanddetei'mining its aiming angle to the taiget I I U l object f this invention to provide aradar annaly z'er functions independently of the iirbbl an output representing the aiming angle nevi e" by iib'tainirig a ratio between the modulation afnpht ac and the carrier wave amplitudeof the t'linsfififtE5?! 4 7 Q of this invention is to provide a radar t aiiifinfg angle'an: zer which is comparatively simple in y e t botli "operation-and "construction and whrch may be packusage;

reading of the followingdes'cription; especially when considered in combination with the accompanying drawing wherein like numerals refer to like parts.

In the drawing: T a

Figure 1 is a bl'ockydiagram showing one'form of the radar aiming angle analyzer;

' "Figure 21is a block diagram showing a second form of the radar aiming angle analyzer; and

. =Figure'3 'is' a geometric diagram illustrating the theory of operation ofthe. analyzer-z; M a o p a The principle employed in the invention is illustrated in Figure 3 whefeinan antenna 1 at some remote location in space radiates electromagnetic energy at a selected radio frequency in a directional manner to provide a beam patter-nhaving a width equalto a "or twice the angle ,8. To

cover a "large search {angle forwardly of the radiating an-' retina and to determine the relative-position of a remote object 'or targefit-fi such as an aircraft, within the radiated "ehergybeam; the beam is systemmatically moved, usually ,bytiltingthe antenna; Assuming the object detecting and locating antenna l employs a conical type scan, as would be the case in the figure 3: arrangement, the aiming direction" ofgthe antenna is located centrally of the conical beam which is'gene'rated.;i Anob'ject, such as an aircraft 2-, loeated within the radiated energy; beam will receive and :refiect'energy but the avera-ge signal strength at the object Will varyfa sa function ofrange. It is alsoof importance to notc'that -t-he amplitude of the modulation envelope on the radio frequency carrier energy will vary .both as a function of error angle and range. The change in amplitude of the modulation envelope due to the change in-range is illustrated infigure 3 wher ein the arc R A at' range R is difierent from, the an: R A at range R even though the e'rroran'gle e of the object locating antenna 1 is the same. Since it is desired tof'm easu're the 51 strength and, hence; independently of a aircraft 2 in Figure 3,;for applying the radio frequency t-ms Pater 2,944,256 Patented July 5, 1960 R A and R B is equal 'to, the ratio between the arcs R A and R 13; which arcs represent the minimum and maximum distances of the radiated energy beam relative to object 2 at two dififerent ranges as the energy beam ofthe aiming angle.

is rotated in the case of the conical scan pattern, vSince the'rati'os or the arcs are substantially constant for a given error'ang'le and at all ranges, it is clear that the percentage of modulation as contrasted with the absolute amplitude of the modulation on the radio frequency carrier energy is solely a function of the aiming error angle Thereforeby detecting the radiated energy at some object, such as aircraft- 2 in the radar search pattern and extracting the modulation envelope from the received energy and obtaining a ratio between the amplitude of the modulation and the amplitude of the carrier wave,- an output representing the percentage of modulation which is proportional to the aiming error angle of the energy beam may be obtained. This is accomplished in the circuit ryof Figures 1 and Z'to provide an arcuate indication Referring to Figure l, the aiming angle analyzer incl-udesan antenna 4 which may becarried, for example by energy transmitted by the remote antenna 1 to a receiver .51 Receiver '5 may be of any. conventional type suitable for operation at the frequencies ofthe garrier wave being detected. The'output 6 of receiver 'Sis applied to an amplifier "7 for supplying power to a pair of band pass filters or tuned circuits 8 and 9 which separate the modulationsignal from the carrier energy as picked up by receiver 5. Tuned circuits 8 and 9 may be of any conventional design so long as theyare sufiiciently selective to pass only the desired band of frequencies. Suitable circuits for'these tuned circuit applications may be found in most any textbook on the subject of Radar Electronics, such asfll/ar Department Technical Manual ll 466, entitled: jRadar Electronics Fundamentals (pages 34 through 37 and 126 through 127) The output of modulation frequency tuned circuit 3 is applied to afilter li through a rectifier 12 to produce a direct current voltage at the output 13 of filial-l1 which has a negative polarity, the amplitude of-whic h is proportional to the amplitude'of the modulation appearing onthe received carrier energy. o i V output of carrier frequency tuned circuit 9 is applied to a filter 1 through a rectifier 15 to provide a direct cuirent voltage at the output 15' of filter 14 which of positive polarity and which has an amplitude propor v tional to the amplitude of the received carrier energy.

Filters 11 and 14 may be conventional condenser-resistor smoothing circuits. Their only function is to improve the rennet thesignal supplied from the rectifiers.

The ratio between the amplitudes ofthe modulation on thecarrier energy and the carrier energy itself for indicating the aiming angle of antenna; is obtained, as shown Figure 1, 'a'servo system which includes a differential serve amplifier 17, a variable potentiometer 18' and a motor 19. Output 13 from filter 11 is applied directly to servo amplifier 17 while output 16 from filter is applied 'to potentiometer 1S.v The amputee off-potentiometei- 18' is fed back to servo amplifier 17 for comparison with the modulation voltage supplied by filter 11. A comparison between the voltages in. the'se rvo amplifier produces an output voltage which is applied to motor =19 through leads Zll for positioning motor shaft-22. Pickup Iof potentiometer 18 is mechanicallyconnected to shaft 22 for positioning to efiectiv'ely obtaina ratio betwecn the voltages appearingasthe outputs hammers 11 and whrein th'e "ratio appears 'a's a shaft rotationa't'motor fi,

r I 2,944,256 v V r only necessary to mechanically drive the arm 24 of a suitable indicator 25 through a direct connection with shaft 22. V

, The circuitry of Figure 2 illustrates a means for indicating the aiming error angle without the use of a direct ratioing device such as is shown in Figure 1. Antenna 26 feeds the radiated energy into a receiver 27. The output of receiver 27 is applied to an amplifier 28 through lead 29 for supplying power to a pair of band pass filters or tuned circuits 30 and 31. Tuned circuit 31 is selected to pass only the carrier wave frequency in the same manner that tuned circuit 9 is employed in the circuit of Figure 1. The output of tuned circuit 31 is rectified by rectifier 32 and then fed into a direct current smoothing filter 33. The output of filter 33 is a direct current voltage, the amplitude of which is proportional to the amplitude of the radio frequency carrier applied to receiver 27. This voltage, which is of negative polarity after being rectified, is fed to receiver 27 as an automatic gain control feed back voltage through lead 34. The function of this feed back to receiver 27 is to stabilize and maintain substantially constant the average amplitude of the carrier wave energy. This, in effect, eliminates the range function in the modulation envelope appearing on the carrier wave energy as transmitted by the object locating antenna 1. Thus, the amplitude of the modulation envelope will vary only as a function of the error angle e.

Tuned circuit 30 in Figure 2 extracts the modulation envelope from the carrier wave energy and feeds the same through a rectifier 35 to provide pulsating direct current of positive polarity in lead 36. The pulsating direct current voltage in lead 36 is applied to a smoothing filter 37 for driving a galvanometer 38, or the like, calibrated to read the aiming angle directly. Where an electrical output is desired in lieu of a mechanical type output as shown in the circuit of Figure 1, the circuit of Figure 2 is perhaps the more desirable.

The invention as illustrated by the circuits of Figures 1 and 2 is useful in any application where it is desired to know the aiming angle of a radar device. An important application is its use in electronic countermeasures devices for indicating not only that you are being detected by a remote radar device such as might be carried in enemy aircraft but also to indicate the aiming angle of that remote radar device. By providing such information, itwill be possible to anticipate an attack while there is still time to take evasive action.

The operation of the aiming error angle detectors or analyzers of Figures 1 and 2 is substantially identical in that both obtain a direct current voltage of one polarity which is proportional in amplitude to the modulation amplitude of the envelope on the radio frequency carrier energy detected by the receiver and a direct current voltage of opposite polarity having an amplitude which is proportional to the amplitude of the radio frequency carin the modulation envelope which is extracted by the use of tuned circuit 30. Since the amplitude of the modulation envelope is thus made independent of range andproportional to the aiming error angle, a servo type ratioing device is unnecessary and the output of smoothing filter 37 may be used directly to drive a galvanometer for indicating the aiming angle.

The radar aiming angle analyzer described herein in connection with Figures 1 and 2 has many useful applications in connection with object detecting and locating de- 4- vices and hence it is subject to many rather obvious alterations, modifications and substitutions for meeting the needs of a specific case. For one example, the alternating current output from the tuned circuits may be operated upon to provide the aiming angle information without first converting to direct current simply by using an A.C. type of ratio indicator. Also, the analyzer may be employed to advantage with any type of target seeking apparatus including infra red devices. Etfective use of the analyzer depends only on a knowledge of the antenna pattern of the target seeker. Therefore, it should be understood that certain alterations, modifications and substitutions including any of those mentioned above may be made to the instant disclosure without departing from the spirit and scope of the invention as defined by the appended claims.

I claim:

1. A device for determining the aiming angle of conical scan radiant energy transmitting apparatus relative to said device comprising, a receiver for detecting the energy transmitted by the transmitting apparatus and reaching said device, a pair of tuned circuits connecting with said receiver, one of said pair of tuned circuits being responsive only to the transmitted radiant energy and producing an output signal proportional to the amplitude thereof, the other of said pair of tuned circuits being responsive only to the scan frequency modulation appearing on the radiant energy detected by said receiver and producing an output signal proportional to the amplitude thereof, means connecting with said tuned circuits and rectifying said output signals to provide voltages of opposite polarity, and means connecting with said last mentioned means and being responsive to a potential developed by the comparison of the rectified output signals for indicating the aiming angle of the transmitting apparatus relative to said device.

2. A device for determining the aiming angle of radiant energy transmitting apparatus relative to said device comprising, a receiver for detecting the radiant energy reaching said device which is transmitted by the transmitting apparatus, a pair of tuned circuits connecting with said receiver, one of said pair of tuned circuits being responsive only to the received radiant energy and producing an output signal proportional to the amplitude thereof, the other of said pair of tuned circuits being responsive only to the scan frequency modulation appearing on the radiant energy detected by said receiver and producing an output signal proportional to the amplitude thereof, means connecting with said tuned circuits and rectifying said output signals to provide voltages of opposite polarity, and ratioing means connecting with said last mentioned means and being responsive to the rectified output signals to provide an output representing the percentage of modulation of the radiant energy and hence the aiming angle of the transmitting apparatus relative to said device.

3. An analyzer for determining the aiming angle of a radiant energy transmitter comprising, a receiver detecting the radiant energy reaching said receiver which is transmitted by said transmitter, a pair of band pass filter circuits connecting with said receiver, one of said pair of filter circuits being responsive only to the received radiant energy and producing an output signal proportional to the amplitude thereof, the other of said pair of filter circuits being responsive only to the modulation envelope appearing on the'radiant energy detected by said receiver and producing an output signal proportional to the amplitude thereof, means connecting with said filter circuits and rectifying said output signals to provide voltages of oppoto the average amplitude of the radiant energy and the other voltage being proportional to the average amplitude of the modulation envelope on the radiant energy, means responsive tothe pair of direct current voltages for obtaining an output representing the ratio therebetween, and indicator means responsive to the last mentiond output providing a direct reading of the transmitter aiming angle relative to the receiver.

5. A wave form analyzer for determining the aiming angle of a radiant energy transmitter comprising, a receiver detecting the radiant energy reaching the receiver which is transmitted by the transmitter, filter means responsive to the received radiant energy and providing a pair of direct current voltages, one voltage being proportional to the average amplitude of the received radiant energy and the other voltage being proportional to the average amplitude of the modulation envelope on the received radiant energy, a potentiometer having said one voltage applied thereto, a difierential amplifier having said other voltage appliedthereto, a servo motor responsive to the output from said differential amplifier, said potentiometer having a pickup arm operatively connecting with said servo motor and electrically connecting with said differential amplifier whereby a ratio of said one voltage with respect to said other voltage is obtained as a shaft output from servo motor, and means operatively connecting with the output shaft of said servo motor indicating the relative aiming angle of said transmitter.

6. A wave form analyzer for determining the aiming angle of a radiant energy transmitter comprising, a receiver detecting the radiant energy reaching said receiver which is transmitted by the transmitter, filter means responsive to the received energy and providing a pair of direct current voltages, one voltage being proportional to the average amplitude of the received energy and the other voltage being proportional to the averageamplitude of the modulation envelope on the received energy, automatic gain control means associated with said receiver and responsive to said one voltage for maintaining the average energy level at the receiver output substantially constant whereby said other voltage vanies only as a function of the radiant energy aiming, angle relative. to the receiver, and indicator means responsive to said 6 7 other voltage and providing a direct reading of the aiming angle of the transmitter.

7. A wave form analyzer for determining the aiming angle of a radiant energy transmitter comprising, means detecting the transmitted radiant energy, filter means responsive to the detected energy and providing a pair of signals, one signal being proportional to the amplitude of the detected radiant energy and the other signal being proportional to the amplitude of the modulation envelope on the detected radiant energy, and indicator means responsive to the pair of signals for obtaining the ratio therebetween and providing adirect reading of the aiming angle of the transmitter relative to the radiant energy detecting means.

' 8. An analyzer for determining the aiming angle of an energy transmitting device comprising, means detecting the transmitted energy at a remote location relative to said device, filter means responsive to the detected energy and providing a pair of signals, one signal being proportional to the amplitude of the detected energy and the other signal being proportional to the amplitude of the modulation envelope on the detected energy, means responsive to the pair of signals and providing an output representing the ratio therebetween, and indicator means responsive to the last mentioned output providing a direct reading of the aiming angle of the transmitting device relative to the energy detecting means.

9. An analyzer for determining the aiming angle of an energy transmitting device comprising, means detecting the radiated energy transmitted by said transmitting device, filter means responsive to the detected energy and providing an output representing the percentage of modulation of the detected energy, and means responsive to said output and indicating the aiming angle of the transmitting device relative to the detecting means.

References Cited in the file of this patent UNITED STATES PATENTS Stodola Oct. 7, 1952 

